This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in light of this purpose, and not as admissions of prior art.
One embodiment of the present invention relates to catalytic hydrogenation of aldehydes to alcohols. Another embodiment of the invention discloses improved catalysts for the catalytic hydrogenation of aldehydes to the corresponding alcohols. A further embodiment discloses processes for the production of the improved catalysts for the hydrogenation of aldehydes to the corresponding alcohols. A further embodiment discloses catalytic processes for hydrogenating aldehydes to the corresponding alcohols utilizing the improved catalyst.
Aldehydes and alcohols are two general classes of organic compounds. Hydrogenation of aldehydes to produce the corresponding alcohols is a major class of organic chemical processes. These processes have long been practiced. In the conventional process the reaction of an aldehyde with hydrogen generally is carried out in the presence of certain reduced metal compounds, which act as hydrogenation catalysts. The conventionally used catalysts for this reaction include copper catalysts, such as copper chromite or copper/zinc oxides; nickel catalysts, such as nickel and nickel compounds with promoters; and cobalt catalysts, such as cobalt compounds with promoters.
The hydrogenation catalysts that have previously been disclosed often exhibit one or more disadvantages when used for commercially hydrogenating aldehydes to alcohols. For example, some of the prior art catalysts are difficult to prepare and have serious toxicity problems associated with their use (e.g. chromium.) Some of catalysts are significantly costly (e.g. cobalt). Some of the catalysts exhibit less than desired selectivity (e.g. nickel and copper) or produce significant amounts of by-products, such as ethers or esters. Such by-products generally must be removed from the hydrogenation product stream prior to subsequent use.
When using nickel catalysts for this process, the principal by-products produced are ethers and hydrocarbons, particularly paraffins. For example, in the catalytic hydrogenation of butyl aldehyde to butanol over a nickel catalyst, butyl ether is produced. The ethers form azeotropes with the alcohol hydrogenation products and water that frequently is present in the product from the feed stream. A substantial effort is necessary to separate these by-products from the alcohols and a significant loss of alcohol is normally encountered.
When copper oxide/zinc oxide catalysts are used for this process, esters are the principal by-product. For example, in the catalytic hydrogenation of butyl aldehyde to butanol over a copper oxide/zinc catalyst, butyl butyrate is produced.
To compensate for the gradual loss of catalytic activity of these hydrogenation catalysts over time, it is conventional practice to increase the reaction temperature. When using reduced copper oxide/zinc oxide catalyst, however, such temperature increases lead to increased formation of the undesired ester by-products, thus further complicating subsequent product purification procedures or necessitating an early change in the catalyst charge.
One widely used catalyst for this reaction is a copper oxide/zinc oxide catalyst as disclosed by U.S. Pat. Nos. 4,876,402 and 4,762,817. These patents disclose the use of alkali metal selectivity enhancers and transition metal selectivity enhancers in combination with the copper oxide and zinc oxide. However, with the technology disclosed therein, either undesired ethers and paraffins tend to be produced or catalytic performance and mechanical strength of the final catalysts are degraded. Further, the leaching rate of the alkali enhancers is high, which often results in a degradation of selectivity over time on stream.
CN 1695802 also discloses catalysts for preparing alcohols from aldehydes in gas phase, which catalysts are produced by a specific two step precipitation process. Catalysts made by this process have reduced selectivity and activity over other prior art catalysts.
Accordingly, a need exists to produce catalysts for the catalytic hydrogenation of aldehydes to corresponding alcohols with improved product selectivity and reduced by-product production while catalytic activity and mechanical strength remain high. Further, improved processes for the production of catalysts that are useful for catalytic hydrogenation of aldehydes to corresponding alcohols and which exhibit improved selectivity and activity are also important.